Reference for a preliminary ruling — Citizenship of the Union — Extradition to a third State of a national of a Member State who has exercised his right to freedom of movement — Scope of EU law — Protection of a Member State’s nationals against extradition — No protection for nationals of the other Member States — Restriction of freedom of movement — Justification based on the prevention of impunity — Proportionality — Verification of the guarantees provided for in Article 19 of the Charter of Fundamental Rights of the European Union